Collimators are frequently used in radiation treatment for narrowing a beam of highly energized particles, referred to as a treatment beam. Some radiation treatment systems use a variable aperture collimator called a multi-leaf collimator (MLC). A multi-leaf collimator is a collimator that is made up of a collection of individual leaves that can move independently in and out of the path of the treatment beam. For conformal radiotherapy, the MLC enables conformal shaping of the treatment beam to match borders of a target. In the MLC, each leaf is powered by its own motor, and has its own displacement gauge to precisely control the position of the leaf. To ensure accuracy, each individual displacement gauge of each leaf must be calibrated by a technician. Additionally, MLCs are highly complex, and susceptible to numerous avenues of failure.
Accuray® Incorporated manufactures another type of variable aperture collimator called the IRIS™ Collimator. The IRIS collimator also has multiple leaves. However, the leaves of the IRIS collimator are all driven together by a single motor to enlarge or decrease the aperture size similar to the operation of an iris diaphragm in a camera. As with MLC collimators, the IRIS collimator occasionally needs to be calibrated by a technician.